<?php
/**
 * Notes: 加解密类
 */

namespace fast;

class Encrypt
{

    protected static $MD5_KEY = 'xiaopzi12355Hkn2Od!@AC#~';

    /**
     * 加密函数
     * @param string $txt 需要加密的字符串
     * @param string $key 密钥
     * @return string 返回加密结果
     */
    public static function encrypt($txt, $key = '')
    {
        if (empty($txt)) return $txt;
        if (empty($key)) $key = md5(self::$MD5_KEY);
        $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.";
        $ikey = "-x6g6ZWm2G9g_vr0Bo.pOq3kRIxsZ6rm";
        $nh1 = rand(0, 64);
        $nh2 = rand(0, 64);
        $nh3 = rand(0, 64);
        $ch1 = $chars{$nh1};
        $ch2 = $chars{$nh2};
        $ch3 = $chars{$nh3};
        $nhnum = $nh1 + $nh2 + $nh3;
        $knum = 0;
        $i = 0;
        while (isset($key{$i})) $knum += ord($key{$i++});
        $mdKey = substr(md5(md5(md5($key . $ch1) . $ch2 . $ikey) . $ch3), $nhnum % 8, $knum % 8 + 16);
        $txt = base64_encode(time() . '_' . $txt);
        $txt = str_replace(array('+', '/', '='), array('-', '_', '.'), $txt);
        $tmp = '';
        $j = 0;
        $k = 0;
        $tlen = strlen($txt);
        $klen = strlen($mdKey);
        for ($i = 0; $i < $tlen; $i++) {
            $k = $k == $klen ? 0 : $k;
            $j = ($nhnum + strpos($chars, $txt{$i}) + ord($mdKey{$k++})) % 64;
            $tmp .= $chars{$j};
        }
        $tmplen = strlen($tmp);
        $tmp = substr_replace($tmp, $ch3, $nh2 % ++$tmplen, 0);
        $tmp = substr_replace($tmp, $ch2, $nh1 % ++$tmplen, 0);
        $tmp = substr_replace($tmp, $ch1, $knum % ++$tmplen, 0);
        return $tmp;
    }

    /**
     * 解密函数
     * @param string $txt 需要解密的字符串
     * @param string $key 密匙
     * @return string 字符串类型的返回结果
     */
    public static function decrypt($txt, $key = '', $ttl = 0)
    {
        if (empty($txt)) return $txt;
        if (empty($key)) $key = md5(self::$MD5_KEY);
        $chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_.";
        $ikey = "-x6g6ZWm2G9g_vr0Bo.pOq3kRIxsZ6rm";
        $knum = 0;
        $i = 0;
        $tlen = @strlen($txt);
        while (isset($key{$i})) $knum += ord($key{$i++});
        $ch1 = @$txt{$knum % $tlen};
        $nh1 = strpos($chars, $ch1);
        $txt = @substr_replace($txt, '', $knum % $tlen--, 1);
        $ch2 = @$txt{$nh1 % $tlen};
        $nh2 = @strpos($chars, $ch2);
        $txt = @substr_replace($txt, '', $nh1 % $tlen--, 1);
        $ch3 = @$txt{$nh2 % $tlen};
        $nh3 = @strpos($chars, $ch3);
        $txt = @substr_replace($txt, '', $nh2 % $tlen--, 1);
        $nhnum = $nh1 + $nh2 + $nh3;
        $mdKey = substr(md5(md5(md5($key . $ch1) . $ch2 . $ikey) . $ch3), $nhnum % 8, $knum % 8 + 16);
        $tmp = '';
        $j = 0;
        $k = 0;
        $tlen = @strlen($txt);
        $klen = @strlen($mdKey);
        for ($i = 0; $i < $tlen; $i++) {
            $k = $k == $klen ? 0 : $k;
            $j = strpos($chars, $txt{$i}) - $nhnum - ord($mdKey{$k++});
            while ($j < 0) $j += 64;
            $tmp .= $chars{$j};
        }
        $tmp = str_replace(array('-', '_', '.'), array('+', '/', '='), $tmp);
        $tmp = trim(base64_decode($tmp));
        if (preg_match("/\d{10}_/s", substr($tmp, 0, 11))) {
            if ($ttl > 0 && (time() - substr($tmp, 0, 11) > $ttl)) {
                $tmp = null;
            } else {
                $tmp = substr($tmp, 11);
            }
        }
        return $tmp;
    }

}